Histones are protein components making up chromatin in association with DNA. Histones are subject to covalent modifications of various enzymes such as, for example, histone deacetylase (HDAC), histone methyltransferase (HMT) and histone acetyltransferase (HAT). Covalent modifications of core histones influence protein-protein interaction and protein access to DNA.
HDACs catalyze deacetylation of lysine residues on histones and other proteins. It is known that low levels of histone-acetylation are associated with repression of gene expression. Therefore, abnormal HDAC activities could destroy the delicate balance in cell regulation. The HDACs belong to four structurally and functionally different phylogenetic classes: class I (HDAC-1, -2, -3, and -8) compounds are closely related to yeast RPD3; class IIa (HDAC-4, -5, -7, and -9) and class IIb (HDAC-6 and -10) share domains with yeast HDAC-1; class IV, recently described (comprising HDAC-11), exhibits properties of both class I and class II HDACs. All the above HDACs are zinc dependent proteases. Class III HDACs have been identified on the basis of sequence similarity with Sir2, a yeast transcription repressor, and require the cofactor NAD+ for their deacetylase function. See, for example, Marielle Paris et al., Histone Deacetylase Inhibitors: From Bench to Clinic, JOURNAL OF MEDICINAL CHEMISTRY 51(11): 3330-3330 (2008).
It has been reported that HDAC activities play an important role in a variety of human disease states. Accordingly, an HDAC inhibitor can provide therapeutic benefits to a broad range of patients. Due to the therapeutic significance, various types of HDAC inhibitors have been developed to date. See, for example, Moradei et al., Histone Deacetylase Inhibitors: Latest Developments, Trends, and Prospects, CURR. MED. CHEM.: ANTI-CANCER AGENTS 5(5):529-560 (2005).
WO 2005/092899 mentions a series of compounds useful for inhibiting HDAC enzymatic activity where the compounds are amino or hydroxyl substituted aniline derivatives attached to various cyclic groups.
There is a continued need to develop new inhibitors to provide appropriate therapy for a variety of disease conditions implicated in HDAC activity.